Nucleic acid based diagnostics is enjoying particularly rapid growth at a time which has seen the overall demand for diagnostic assays continue to rise. Undoubtedly, this growth has been hastened by the increased pressure on medical professionals to contain costs. In response, the medical establishment is placing a growing emphasis on early intervention and prevention. Accordingly, assays which alert clinicians to a disease susceptibility have engendered strong interest. Nucleic acid based diagnostic assays promise to play a leading role in the expanding market for diagnostic assays.
Perhaps the single most critical step in nucleic acid based diagnostic assays is the selective hybridization of an oligonucleotide to its complementary target. A particularly favored means of accomplishing this has been through the use of solid phase supports. Solid phase DNA probe hybridization typically involves the direct or indirect covalent attachment of a synthetic "capture" oligonucleotide to a solid phase. The capture oligonucleotide is brought in contact with a sample comprising DNA or RNA under stringent hybridization conditions to promote duplex formation between the capture oligonucleotide and a complementary nucleic acid in the sample. Covalent attachment procedures require multiple chemical steps (which effect yield) and special handling equipment for the solid phase. Thus, it is costly and troublesome to change the particular oligonucleotide attached to the solid support. Previously, the severity of these problems was partially overshadowed by the relatively high cost and labor-intensive assay formats then in use. Today, however, the high capacity, high throughput, automated assay systems demanded by clinical laboratories has drawn increasing attention to the issues of manufacturing cost and complexity.
Application WO 90/10717 describe an attempted solution to the problem. In that publication, a nucleic acid tail of known sequence is attached to a capture oligonucleotide and the complement to the tail portion is covalently attached to the solid phase. Each new capture oligonucleotide shares the same tail such that the same solid phase can be used for all products. However, this approach requires that the tail oligo-complement hybrid be stable under the conditions of the sample hybridization. Since the sample hybridization conditions may vary with each new sample target, this approach requires a long region of complementarity to accommodate the high melting temperatures of possible target-oligonucleotide hybrids. Unfortunately, these long oligonucleotides have an increased risk of binding to non-target nucleic acids. Moreover, the secondary structural characteristics of long single strand nucleic acids can hinder access to the target.
Holodniy et al. (Biotechniques, 12:36-39 (1992)) describe the detection and quantification of gene amplification products using a solid phase which is non-covalently coated with avidin. However, in that system hybridization is accomplished at 42.degree. C. , a hybridization temperature often too moderate for high stringency hybridization.
Accordingly, what is needed in the art is a solid-phase hybridization apparatus which is tolerant of high-temperature and high stringency hybridization conditions and which can be readily, quickly, and inexpensively adapted to detect a variety of nucleic acid targets. The present invention provides these and other advantages.